Abstract: We study the luminescence of unintentionally doped and Si-doped
In$_x$Ga$_{1-x}$N nanowires with a low In content (x<0.2) grown by molecular
beam epitaxy on Si substrates. The emission band observed at 300 K from the
unintentionally doped samples is centered at much lower energies (800 meV) than
expected from the In content measured by x-ray diffractometry and energy
dispersive x-ray spectroscopy. This discrepancy arises from the pinning of the
Fermi level at the sidewalls of the nanowires, which gives rise to strong
radial built-in electric fields. The combination of the built-in electric
fields with the compositional fluctuations inherent to (In,Ga)N alloys induces
a competition between spatially direct and indirect recombination channels. At
elevated temperatures, electrons at the core of the nanowire recombine with
holes close to the surface, and the emission from unintentionally doped
nanowires exhibits a Stark shift of several hundreds of meV. The competition
between spatially direct and indirect transitions is analyzed as a function of
temperature for samples with various Si concentrations. We propose that the
radial Stark effect is responsible for the broadband absorption of (In,Ga)N
nanowires across the entire visible range, which makes these nanostructures a
promising platform for solar energy applications.

Comments:

This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters (2016), copyright (C) American Chemical Society after peer review. To access the final edited and published work see this http URL